摘要:

The fundamental characteristics of heterodyne and nonheterodyne imaging laser radars are presented in terms of information content, structual complexity, and sensitivity limits. The sensitivity characteristics of heterodyne and nonheterodyne laser receivers are quantitatively compared. When feedback amplification or low‐noise multiplication gain is available in the receivers, the direct detection of laser signals can approach or even surpass the sensitivity or coherent detection. The concept of ‘‘self‐homodyne’’ is introduced and its potential application to laser radar measurements is addressed.

ISSN:0034-6748    

DOI:10.1063/1.1138921

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

For heterodyning two optical beams it is necessary to obtain two almost coherent waves. Rather than using an extremely stable laser source, it is possible to split the beam from a single source and use a modulator to shift the frequency of one of the waves. The heterodyne signal generated is at the frequency of modulation, thus, it is susceptible to rf interference by the high modulation voltage. Using two electro‐optical modulators, one can utilize the signal at the sum or difference frequency at which no high voltage is present. It is shown that using a single source and two modulators one obtains a signal without any interference leakage. Thus it is possible to measure easily the frequency response of photodetectors up to high frequencies. This configuration also doubles the frequency range obtainable from a single modulator. The theoretical expressions for the intensities at the various frequencies are presented. Noise equivalent power (NEP) measurements of heterodyne signals performed using this setup are very close to the theoretical limit.

ISSN:0034-6748    

DOI:10.1063/1.1138922

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A compact discharge‐pumped XeCl laser is described with high efficiency and reliability at low operating pressures below 2 atm. Using 65.8% Ne, 30.0% Ar, 4.0% Xe, and 0.2% HCl mixture, the maximum total efficiency of 0.9% was obtained at the total gas pressure of 1.8 atm and the charging voltage of 18 kV. That efficiency was fairly high for the low operating pressure and the compact size of the laser chamber. The shot‐to‐shot reproducibility of the laser pulse was excellent, and the laser energy stability was within ±4%.

ISSN:0034-6748    

DOI:10.1063/1.1138923

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A krytron‐based electrical circuit of a &lgr;/4 and &lgr;/2 voltage pulse generator for a Pockels cell incorporated in a self‐injected and cavity dumped short‐pulse laser source is described. The circuit supplies three independent high‐tension pulses having amplitudes between 1 and 2.5 kV, fall and rise times <2 ns, and jitter <2 ns. Pulse durations and interpulse distances are adjustable.

ISSN:0034-6748    

DOI:10.1063/1.1138924

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A four‐filter ultraviolet radiometer for measuring stratospheric ozone is described. The payload is launched aboard a Super‐Loki rocket to an apogee of 70 km. The instrument measures the solar ultraviolet irradiance over its filter wavelengths as it descends on a parachute. The amount of ozone in the path between the radiometer and the sun is calculated from the attenuation of solar flux using the Beer–Lambert law. Radar at the launch site measures the height of the instrument throughout its flight. The fundamental ozone value measured by the ROCOZ‐A radiometer is the vertical ozone overburden as a function of geometric altitude. Ozone measurements are obtained for altitudes from 55 to 20 km, extending well above the altitude range of balloon‐borne ozone‐measuring instruments. The optics and electronics in the radiometer have been designed within relatively severe size and weight limitations imposed by the launch vehicle. The electronics in the improved rocket ozonesonde (ROCOZ‐A) provide essentially drift‐free outputs throughout 40‐min ozone soundings at stratospheric temperatures. The modest cost of the payload precludes recovery and makes the instrument a versatile tool compared to larger ozonesondes.

ISSN:0034-6748    

DOI:10.1063/1.1139209

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A multichannel vacuum ultraviolet spectrometer has been constructed to provide time‐resolved measurements of line radiation from a plasma. The spectrometer may simultaneously view up to 40 preselected narrow spectral bands or lines from a common viewing chord in a wide spectral region (∼60–450 nm) with the maximum frequency response limited to 80 MHz by the photomultipliers and 350 kHz by the data‐acquisition system. Rapid reselection of impurity lines is facilitated by the use of multiple slits cut in a metal foil placed at the Rowland circle of the instrument. Due to the limitation imposed by the present fiber‐optic coupling to the plasma the results to date are from impurity wavelength in excess of about 220 nm.

ISSN:0034-6748    

DOI:10.1063/1.1138870

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A dual homodyne detection system for measuring scattered radiation from plasmas has been fabricated. The system is operative in the far‐infrared regime, and with it the power spectral distribution of the scattered radiation in the upper and lower sidebands with respect to the frequency of the incident wave can be obtained. Theory of operation and experimental results for simulated radiation fields are given.

ISSN:0034-6748    

DOI:10.1063/1.1138871

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new method for observing a nonlinear wave is proposed and illustrated with sample measurements. Observations are performed by using the time‐of‐flight method by counting the temporal upper hybrid wave packets which pass through the gap between two antennae. Two types of nonlinear waves were found in the experiment. One is outlined in the Korteweg de Vries equation by its behavior through the dispersion relation and the other behaves as a shock wave which represents the relaxing oscillation. The method of observation and the characteristics of the nonlinear waves are discussed circumstantially.

ISSN:0034-6748    

DOI:10.1063/1.1138872

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A system has been developed specifically for the calibration and development of thermal ion instrumentation. The system is optimized to provide an extended, approximately 80‐cm2beam, with usable current rates ∼1 pA/cm2at beam energies as low as 1 eV, with much higher values available with increasing energy. The beam energy spread is typically less than 2 eV/charge and the average angular divergence is approximately 2.5°. A tandem electrostatic and variable geometry magnetic mirror configuration within the ion source optimizes the use of the ionizing electrons, thus decreasing the gas and nonthermal electron throughput to the instrument chamber while improving the current density uniformity. The system is integrated under microcomputer control to allow automatic control and monitoring of the beam energy and composition and the mass‐ and angle‐dependent response of the instrument under test. The data can be transmitted in nearly real time to the interested investigators for comparison with expected results over existing computer networks. The system is pumped by a combination of carbon vane and cryogenic sorption roughing pumps and ion and liquid‐helium operating pumps. This allows testing and final calibration of flight instrumentation in an ultraclean environment.

ISSN:0034-6748    

DOI:10.1063/1.1138873

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Reported here is the design and experimental investigation of the performance characteristics of a new time‐of‐flight (TOF) mass spectrometer. The instrument combines the advantages of beam deflection for ion pulse formation with an electrostatic analyzer which reduces the energy spread of the ions admitted to the TOF region. The instrument is able to use ion sources which cannot be pulsed on a time scale suitable for conventional TOF analysis (e. g., chemical ionization sources). Improved mass resolution is demonstrated over a wide mass range such that all of the ions are in focus simultaneously. A resolution of 982 (full width at half‐maximum) is achieved for the molecular ion peak of perfluorotributylamine atm/z614. A preliminary investigation of a proposed technique for collecting information typically obtained by tandem mass spectrometry (MS/MS) has also been conducted using this instrument. This new method, named time‐resolved ion kinetic energy spectrometry (TRIKES), combines time‐of‐flight (velocity) and kinetic energy analysis of undissociated parent ions and daughter ions which are products of decompositions occurring between the ion source and electrostatic analyzer. Unit resolution of the daughter ions produced upon metastable decomposition of the molecular ion ofn‐decane has been achieved in constant parent scans. The realization of rapid time‐of‐flight data collection rates in TRIKES may yield improved data collection rates in MS/MS.

ISSN:0034-6748    

DOI:10.1063/1.1138874

出版商:AIP    

年代:1986

数据来源: AIP